— Bearings & Fits
Bearing Types
| Type | Radial Load | Axial Load | Typical Use |
|---|---|---|---|
| Deep groove ball | High | Low–Moderate (both directions) | General-purpose shafts, motors, gearboxes, pumps — the default choice for light-to-moderate loads |
| Angular contact ball | Moderate–High | High (one direction; paired for both) | High-speed spindles, gearbox pinion shafts, precise axial location under combined load |
| Cylindrical roller | Very high | None (standard type) | Heavy radial loads at high speed — motors, gearboxes, machine tool spindles |
| Tapered roller | High | High (one direction; opposing pairs for both) | Wheel hubs, differentials, gearboxes with combined radial/thrust loads |
| Spherical roller | Very high | Moderate | Heavy machinery with misalignment or shaft deflection — conveyors, vibrating screens |
| Needle roller | High (compact envelope) | None (standard type) | Severe radial-space restrictions — transmissions, rocker arms, universal joints |
| Thrust (ball or roller) | None–Low | High | Axial-dominant loads — vertical shafts, gear thrust faces, crane hooks |
ISO Fit Selection for Bearings
ISO 286 defines a tolerance as a letter (position of the tolerance zone) + a number (IT grade, zone width). Bearing engineering uses the hole-basis system: bore/OD tolerance is effectively fixed by the bearing, so shaft and housing bore tolerances are chosen to produce the desired fit. Key rule: the ring experiencing a rotating load (relative to load direction) needs an interference or tight transition fit to prevent it creeping in its seat; the ring under a stationary load gets a clearance fit so it can float axially for thermal expansion.
| Application | Inner Ring (Shaft) Fit | Outer Ring (Housing) Fit | Why |
|---|---|---|---|
| Rotating shaft, stationary housing (motors, pumps, gearboxes) | j5/k5 (light-normal), m5/m6 (heavy), up to p7 (very heavy/large) | H7/H8 (clearance) or J7 (slight clearance) | Inner ring rotates with the load — needs interference; outer ring is stationary — clearance allows axial float |
| Stationary shaft, rotating housing (wheel hubs, conveyor pulleys) | h6 (clearance) | K7 (transition, normal-heavy) or M7/N7/P7 (heavier loads) | Housing rotates with the load — needs interference; shaft is stationary — clearance is fine |
Roller bearings typically run one tolerance grade tighter than ball bearings at each shaft-size break, since they need less internal clearance margin. A loose fit on the ring carrying the rotating load causes it to creep on its seat, generating wear debris and fretting. See the Press-Fit / Interference Fit calculator to check the resulting contact pressure and stress for a given interference.
Metric Bearing Bore Code
For standard metric bearings (e.g. the 60xx/62xx/63xx deep groove ball series), the last two digits of the designation are the bore code:
| Bore Code | Bore Diameter |
|---|---|
| 00 | 10 mm |
| 01 | 12 mm |
| 02 | 15 mm |
| 03 | 17 mm |
| 04 through 96 | Bore code × 5 mm (e.g. 6205 → 05 × 5 = 25 mm) |
Non-standard/odd bores (below 10 mm, or sizes like 22/28/32 mm that don't fit the coded scheme) are given uncoded, separated by a slash — e.g. 62/22 for a 22 mm bore.
L10 Life & Lubrication
L10 life is the number of revolutions (or hours at constant speed) that 90% of a population of identical bearings will complete or exceed before the first sign of fatigue — a statistical prediction, not a guarantee for an individual bearing. Field life is often governed by contamination, misalignment, or lubrication failure rather than fatigue. Roughly 80–90% of rolling bearings are grease-lubricated (simpler to retain/seal, adequate for most speed/temperature ranges); oil is used when speed, temperature, or heat-removal needs exceed grease's capability. Grease relubrication intervals shorten sharply with heat — a common rule of thumb is the interval roughly halves for every 15°C rise above 70°C.
See the Bearing Life (L10) calculator to compute L10 life from a bearing's dynamic load rating and applied load.